docs: def findFirstHref(link_attrs_list, target_rel):
      """Return the value of the href attribute for the first link tag
      in the list that has target_rel as a relationship."""
      # XXX: TESTME
      matches = findLinksRel(link_attrs_list, target_rel)
      if not matches:
          return None
      first = matches[0]
      return first.get('href')